The Collaborative International Dictionary of English v.0.48:

Inconclusive \In`con*clu"sive\, a.
   Not conclusive; leading to no conclusion; not closing or
   settling a point in debate, or a doubtful question; as,
   evidence is inconclusive when it does not exhibit the truth
   of a disputed case in such a manner as to satisfy the mind,
   and put an end to debate or doubt.
   [1913 Webster]

         Arguments . . . inconclusive and impertinent. --South.
   -- In`con*clu"sive*ly, adv. -- In`con*clu"sive*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

inconclusiveness
    n 1: the quality of being inconclusive [ant: conclusiveness,
         decisiveness, finality]